It is analog because it varies it's internal resistance linearly to create 5VDC on the output.

A SMPS (switching mod power supply) turns a output transistor on/off (the two most efficient states for a switching device) and averages the voltage around the voltage set point. As a result, it is much more efficient, if noisier.

A DC voltgae of 5V (lets say o/p of 7805).
Is it digital or analog.
Analog because it is continuous signal over entire time range.?????????

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A DC voltage level is neither analog nor digital, as those labels refer to how information is processed. A DC voltage, as in a supply voltage, isn't information. However, the 7805, being a linear regulator, would be considered an analog circuit.

so can we reach at some conclusion
its analog (not 7805, its general dc voltage)
digital
both?????????

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Analog/digital refers to signal and signal requires change (in voltage, current, whatever). If the change is continuous, the signal is analog. If the change is discrete, the signal is digital. An unchanging voltage across a load will create a steady current, which isn't a signal and so isn't analog or digital.

Power supply current are exactly not referred as Digital or analog but to confuse people they are stated as Digital supply or Digital ground or analog ground. So n00bs tend to believe it is a digital supply or analog supply which a standard 7805 can be refereed to both it is just a power supply regulator.

It's how they are used or in which type of circuit they supply power gives the name Digital or Analog.

On the other hand, a supply can be said a digital supply if the regulator circuitry or control uses a digital processor to do all the sensing and controls. Then it is a mostly Digital. Or say an SMPS is sorta digital but analog current do exist with in it.

To confuse matters even worse, the terms "analog supply" and "digital supply" are also used in the context of "the supply that provides power to the analog (or digital) circuitry". In this use, the supply isn't categorized by how it works, but what it supplies power to. This usage is common in situations in which a designer is working with a mixed-signal system, particularly on an integrated circuit. Each supply normally has different requirements, particularly in terms of tolerable noise level. Sometimes it is important that the analog supply be linear while the digital supply can be a switch-mode, but it is not uncommon for both to have to be linear in order to meat the noise requirements (which are usually driven by the need to keep noise in the analog circuitry to a minimum with the noise coupling from the digital sections into the analog sections putting limits on the digital supply tighter than what the digital circuitry, itself, demands.